https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71463
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
__warn_unused_result__ is only used when Fortified is used. Which is not the
default unless you are using a distro compiler.
#if defined _FORTIFY_SOURCE && _FORTIFY_SOURCE > 0 \
&& __GNUC_PREREQ (4, 1) && defined __OPTIMIZE__ && __OPTIMIZE__ > 0
# if _FORTIFY_SOURCE > 1
# define __USE_FORTIFY_LEVEL 2
# else
# define __USE_FORTIFY_LEVEL 1
# endif
#else
# define __USE_FORTIFY_LEVEL 0
#endif
.....
/* If fortification mode, we warn about unused results of certain
function calls which can lead to problems. */
#if __GNUC_PREREQ (3,4)
# define __attribute_warn_unused_result__ \
__attribute__ ((__warn_unused_result__))
# if __USE_FORTIFY_LEVEL > 0
# define __wur __attribute_warn_unused_result__
# endif
#else
# define __attribute_warn_unused_result__ /* empty */
#endif
#ifndef __wur
# define __wur /* Ignore */
#endif
